Cytoplasmic male sterility (CMS) is the maternally inherited inability to produce functional pollen and has been successfully used in commercial production of hybrid seed, thus avoiding the drawbacks of hand or mechanical emasculation. (Kaul, M. L. H. 1988. Male sterility in higher plants. Springer-Verlag, Berlin). More than 40 sources of CMS have been identified and classified into three major groups: CMS-T (Texas), CMS-S (USDA) and CMS-C (Charrua) type cytoplasm. (Beckett, J. B., Crop Sci., 11:724-726, 1971).
The Rf restorer genes, which impart and restore fertility to plants that are cytoplasmic male sterile, have been cloned or mapped at high resolution from several plant species. To date, eleven Rf genes have been cloned or mapped to high resolution. Most cloned restorer genes, except Rf2 and Rf4 in maize and Rf17 and Rf2 in rice, encode different pentatricopeptide repeat (PPR) proteins. The PPR proteins contain two to 27 repeats of 35 amino acids, called PPR motifs (Small, I. D. and Peeters, N., Trends Biochem. Sci., 25:46-47, 2000). Many PPR proteins are targeted to mitochondria where the CMS-associated genes and products are located (Lurin, C. et al., Plant Cell, 16:2089-2103, 2004).
In maize, the genes encoding the restorer of the S type cytoplasm of CMS behave as a gametophytic trait. Maize plants with CMS-S type cytoplasm are restored by the single dominant gene, Rf3, which was mapped to genomic fragments of several centimorgans in length on chromosome 2, via marker sequences. (Kamps and Chase, Theor. Appl. Genet., 95:525-531, 1997; Tie, S., Xia, J., Qiu, F. and Zheng, Y. Plant Mol. Biol., 24:71-80, 2006; Zhang, Z. and Zheng Y. Mol. Gen. Genomics., 276:162-169, 2006). Traditional breeding applications deploy the use of markers that are associated at great distance with the Rf3 and rf3 alleles to restore or to provide cytoplasmic male sterility in maize plants, respectively. (Laughnan, J. R. and Gabay, S. J. 1978. Nuclear and cytoplasmic mutations to fertility in S male-sterile maize. pp. 427-446. In: Maize Breeding and Genetics). Furthermore, heterozygous (Rf3/rf3) CMS-S plants are semi-fertile, shedding approximately 50% abortive collapsed pollen containing the rf3 allele and approximately 50% starch-filled fertile pollen containing the Rf3 allele. The rf3 allele in Rf3/rf3 plants cannot be transferred to progeny through sterile pollen, and generate sterile plants in an F2 generation. (Tie et al., Plant Mol. Biol. Rep., 24: 71-80, 2006). This type of inheritance makes it difficult to collect accurate phenotypic data from an F2 mapping population. As such, traditional methods for using or identifying the dominant and recessive alleles of the Rf3 genes are labor and time-intensive.
Therefore, there exists a need exists for compositions and methods that can be utilized to isolate and identify protein sequences that are encoded by the cytoplasmic male sterility restorer (Rf3) and cytoplasmic male sterile (rf3) gene sequences, and for methods of detecting the cytoplasmic male sterility restorer (Rf3) and cytoplasmic male sterile (rf3) gene sequences in plants.
Accordingly, the present disclosure provides an alternative approach for the isolation and identification of polynucleotide and protein sequences encoded by the Rf3 allele that result in the cytoplasmic male sterility restorer phenotype, and subsequent sequence modifications encoded by the rf3 allele that result in the cytoplasmic male sterile phenotype. The discovery of these sequences can be utilized in cytoplasmic male sterile systems for breeding hybrid plants of a number of crop species. Furthermore, the application of this system can result in cost savings and increased efficiency. For example, deployment of a cytoplasmic male sterile system in corn can be used to eliminate the expensive and laborious task of detasselling corn plants to avoid self pollination.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification.